The best item that you can use to store hot water would be a hot water cylinder. You can store hot water for several days with the help of this system since it is greatly insulated and can retain heat. A gas boiler or electric immersion heater is used to heat up hot water inside the cylinder.

There are 2 main types of hot water cylinders for domestic use:

  • Vented cylinder
  • Uvented cylinder

Moreover, there are also other ways to describe cylinders:

  • Single coil – In case there is only 1 external source of heat, the single coil cylinder will be used
  • Twin coil – In case of two sources of heat, such as solar water heating panels or a wood burner together with a gas boiler, a twin coil will be used.

While the gas boiler includes a heat output of 15kW-24kW, we need to know that the majority of hot water cylinders include the option of an electric immersion heater, often 3kW, which will heat the water more slowly. Compared to other forms of heating, like natural gas, it is much more expensive to use an electric immersion heater, and will also take more time to heat up the water.

Vented Cylinder

A vent pipe and a cold water tank are used to connect vented cylinders. Traditionally used in gravity fed heating systems, the vented cylinders are open to the pressure of the atmosphere.

The vented system will produce hot water at about 0.2 bar. This is nearly ten percent of the general water pressure provided by unvented system. Considering the fact that vented cylinder does not require to be built to support such high pressure, they are cheaper compared to unvented systems. However, a hot water overflow tank and a separate cold water tank should be purchased.

Unvented cylinders

These types of cylinders offer a powerful flow of hot water since they are pressurized to main water pressure. Since they have to support higher pressure, they cost more than vented systems.

You will find an expansion vessel in the unvented cylinders, which is used to allow any pressure to be relieved. In case the hot water pressure becomes excessive, the unvented cylinders rely on a tundish that helps in releasing the pressure.

Single Coil Cylinder

The majority of the heating systems used in domestic purposes include a single coil cylinder. The heated water included in a gas or oil-fired boiler is taken and circulated in the cylinder to heat up the water stored in it. The valve of the cylinder will switch off the circulation of the hot water from the boiler as soon as the cylinder has reached the desired temperature.

Water may also be heated using 3kW electric immersion heather in case the boiler is turned off.

Twin Coil Hot Water Cylinder

In case there are 2 different ways of heating water, the twin coil hot water cylinders are employed. A lower coil is used by the solar water heating panels on the right of the image to heat up as much of the water as possible.  Throughout the day period, the solar energy will heat up the stored water. Nearly 90% or more of the hot water needed will be heated on a summer`s day. This percentage will drop to only 10-20% on a cold winter`s day. By providing heater water to the upper coil, the secondary heating system will supplement this action. The boiler will switch off as soon as it has heater the water in the top half of the cylinder to the wanted temperature.

To explain the twin system, we need to understand that the lower coil will be the first to heat the water. In case it does not manage to reach the desired temperature the higher coil heating will be employed.

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